ACADEMY OF SCIENCES. 1) 
Eocene Tertiary, and most of them much less far. But some included in the 
comprehensive genus “ Helix,” are found fossil in the Eocene of Nebraska, 
ete., sufficiently like living American forms to be considered the ‘‘Darwinian’’ 
ancestors of perhaps the whole of them! Or we may go back only to the 
Miocene epoch, when trees scarcely distinguishable from the Californian 
Redwood and Libocedrus flourished in Greenland and Spitzbergen, between 
lat. 70° and 78-. What is more natural than to suppose that land-shells also, 
like those now living among our redwoods and cedars, existed in the shade of 
those trees? I have no doubt that such will yet be found fossil in the lignite 
beds of the Arctic Zone. 
It is easy then to see, that having their central position (if not their origin) in 
points so near the present North Pole, the subsequent gradual cooling of those 
regions, which is supposed to have driven the living species of Redwoods 
southward to California and Japan, as well as other trees into Europe, would, 
if a slow change of climate, also drive southward the land-mollusca ‘‘at a 
snail’s pace’ into the same regions, where we now find their descendants 
occupying countries, which are about equidistant in longitude, around the 
northern hemisphere, in lats. 40°-650°. 
We have strong confirmation of this theory, in the well-known distribution 
of circumpolar species of land-shells southward, on both continents, along 
meridians of similar temperature, and along mowntain ranges (especially those 
running southward, as in America), and which are supposed to have thus 
migrated south during the ‘‘ Glacial Epoch.”’ 
Besides these two groups, the ‘‘ circumpolar’’ and the ‘‘ representative ’’ 
species, we also have on the west slope a very few of the Eastern American 
types. I do not, however, consider these as evidence of a migration westward, 
but would explain their occurrence as proving a former existence of ancestors 
common to both, in the middle regions of Oregon and Nebraska, where are 
found so many tertiary remains of animals that once inhabited both regions, 
before the Rocky Mountains became a barrier to migration, or caused different 
climates on the two slopes. 
The few fossil land-shells yet found in California are not sufficiently abundant 
or ancient to furnish data for their geological history. The fresh water forms, 
however, which I hope at some future time to describe and illustrate, indicate 
avery different and more tropical group in the Pliocene and Miocene strata. 
The occurrence of Pupa and Conulus in the carboniferous strata of Nova 
Scotia, shows that land-shells existed long before the Eocene period. 
The great northern glacial drift, and local glaciers farther south, have so 
generally destroyed the softer tertiary deposits that it must be long before the 
routes of migration can be traced from Greenland southward, but as tertiary 
land plants are found there fossil, some similar deposits must have escaped 
elsewhere in the intermediate regions. Species much like the living ones 
of California may be expected to occur in the Pliocene of British Columbia. 
There can be no doubt that the local migration has been westward along 
this coast, from the facts before stated as to the occurrence of species in the 
coast ranges and islands, which are unquestionably not older than Pliocene in 
age, while their allies in the Sierra Nevada may have existed there since the 
Eocene, but at a greater elevation than they are now found. As they move 
’ 
